1. Field of the Invention
The present invention relates to a throttle body which controls an amount of air moving toward an internal combustion engine, and more particularly to a tandem valve type throttle body which is provided with a first throttle valve controlled so as to be opened and closed by an accelerator within an intake passage provided in the throttle body, and a second throttle valve of normally open type arranged in an upstream side of the first throttle valve in the intake passage and operated so as to be closed by an electromagnetic actuator or the like.
2. Description of Conventional Art
A conventional tandem valve type throttle body is shown in Japanese Utility Model No. 2546063.
In accordance with the tandem valve type throttle body mentioned above, there is disclosed a structure in which valve opening directions of the first throttle valve and the second throttle valve arranged in the upstream side of the first throttle valve are set to the same direction, a full-open position of each of the throttle valves is set to a rotational angle before each of the throttle valves matches to an axial line of the intake passage, an outer periphery of each of the throttle valves as seen in an axial direction of the intake passage at the rotational angle position is set to be within a range of a diameter of a throttle valve shaft, and a distance between both the throttle valve shafts is set to be shorter than twice a radius of the throttle valve.
Then, the first throttle valve is operated so as to be opened and closed by the accelerator, and the second throttle valve is operated so as to be closed by the electromagnetic actuator or the like. For example, at a time of traction control or the like, the second throttle valve is forcibly closed, whereby a torque of the engine is reduced at a time when a slip is generated.
In accordance with the conventional tandem valve type throttle body, it is possible to reduce a length of the intake passage in the throttle body in a longitudinal direction, however, there are the following problems.
First of all, the valve opening directions of the first throttle valve and the second throttle valve are set to be the same direction. Accordingly, in particular, a rotational direction of a second throttle valve lever which is attached to an end portion of the second throttle valve shaft for rotating the second throttle valve is definitely determined, and a freedom of design of the second throttle valve lever is largely restricted.
This is not preferable particularly for a motor cycle because the throttle body is arranged within a narrow limited space between the engine and a fuel tank or the like. That is, the freedom of design of the second throttle valve lever is limited by restricting the rotational direction of the second throttle valve lever to the same direction as the opening direction of the second throttle valve.
Secondly, the full-open positions of the first throttle valve and the second throttle valve are set to the rotational angle position before matching to the longitudinal axial line of the intake passage, and it is impossible to arrange both the throttle valves in parallel to the longitudinal axial line of the intake passage.
In accordance with this structure, a gap is formed between an upstream end portion of the first throttle valve and a downstream end portion of the second throttle valve and it is impossible to sufficiently obtain an effect of rectifying an air flowing through the intake passage, so that it is hopeless to improve an air intake efficiency.
The present invention is made by taking the problem mentioned above into consideration, and an object of the present invention is to provide a tandem valve type throttle body which does not restrict a closing direction of a second throttle valve to a single direction, can achieve an improvement of an intake efficiency at a time of fully opening the first and second throttle valves, and can reduce an entire length of a throttle body.
In order to achieve the object mentioned above, in accordance with a first aspect of the present invention, there is provided a tandem valve type throttle body comprising:
an intake passage provided through an inner portion of the throttle body;
a first throttle valve which opens and closes the intake passage interlocking with an accelerator;
a second throttle valve of normally open type which is disposed in an upstream side of the first throttle valve and is operated so as to be closed,
the first throttle valve and the second throttle valve being arranged within the intake passage,
wherein the first throttle valve is formed in a butterfly type and is attached to a first throttle valve shaft which is rotatably supported to the throttle body across the intake passage,
the second throttle valve is formed in a butterfly type, is attached to a second throttle valve shaft which is rotatably supported the throttle body across the intake passage, with a pitch between both the throttle valve shafts being set to be twice a radius of the throttle valves or less, and
a notch portion is formed in the second throttle valve in correspondence to an interference portion on planes of both the throttle valves at a time of fully opening both the throttle valves.
Further, in accordance with a second aspect of the present invention, there is provided a tandem valve type throttle body as recited in the first aspect mentioned above, wherein centers in rotation of the first throttle valve shaft and the second throttle valve shaft, and centers of thickness portions of the first throttle valve and the second throttle valve are arranged on an axial line in a longitudinal direction of the intake passage, and both the throttle valves in directions of fluid flows within the intake passage are arranged within a surface of projection in the directions of the fluid flows of both the throttle valve shafts, at a time of fully opening the first throttle valve and the second throttle valve.
In accordance with the first aspect of the present invention, since the notch portion is formed in the second throttle valve in correspondence to the interference portion on the planes of both the throttle valves at a time of fully opening the first throttle valve and the second throttle valve, the operation of the second throttle valve in the closing direction may be performed in any one of a clockwise direction and a counterclockwise direction, and the closing direction is not limited to one direction.
Further, it is possible to reduce the pitch between both the throttle valve shafts in correspondence to the interference portion, whereby it is possible to reduce an entire length of the throttle body.
Further, in accordance with the second aspect of the present invention, since the centers in rotation of the first throttle valve shaft and the second throttle valve shaft, and the centers of the thickness portions of the first throttle valve and the second throttle valve are arranged on the axial line in the longitudinal direction of the intake passage, and both the throttle valves in the directions of the fluid flows within the intake passage are arranged within the surface of projection in the directions of the fluid flows of both the throttle valve shafts, at a time of fully opening the first throttle valve and the second throttle valve, it is possible to increase an effect of rectifying the fluid flowing within the intake passage and it is possible to improve an intake efficiency.